Using my cell phone camera and lots of labels works for me, too. It is so frustrating to get them out of order.
I have a small sewing area and small house without a wall for even a wall to hang a design wall. I lay out a flannel sheet on a table then lay out the blocks. Since I rarely have time to finish the assembly I have taken pictures which I really like. Then I fold up the sheet over the blocks carefully. I can unfold as I am ready to work on the top.
I do both suggestions, pinning to keep in order and marking with sticky notes.
I like your flannel sheet idea, Newby. If you fold carefully or roll it up you could unfold a row at a time as you sew.
I use a design wall.
I have wooden clothes pins. I mark each one by row and number,apply to the blocks in order,then it's easier to keep them where they should go. I'm famous for sewing stuff upside down and backwards...repeatedly!
I use the small yard sale type stickers with the A, b, c, going down and numbers going a cross. A-1, A-2 etc. I also take pictures a a rearrange them and finally after I settle on the final layout.
No need for fancy pins - if you have flower head pins you can write on the "flower" part with a sharpie